1. Field of the Invention
The present invention relates to an alcohol concentration estimation and detection apparatus for an engine. More particularly, the present invention relates to an alcohol concentration estimation and detection apparatus which is operable to estimate and detect an alcohol concentration of a mixed-content fuel, based on an output signal of a crank pulse rotor configured to rotate in synchronism with a crankshaft of the engine.
2. Description of the Background Art
In recent years, biofuels, aimed at providing more earth-friendly fuels, have become popular as fuels for operating internal-combustion engines for automobiles and motorcycles. Gasoline fuel mixtures containing ethyl alcohol, which may be extracted from sweet potatoes, corn and/or other plant material, may be used as one type of power source containing a biofuel.
A vehicle ready for such an alcohol-containing fuel mixture as described above is generally called a Flex-Fuel Vehicle (FFV), and in order to normally carry out suitable engine control such as control of the ignition timing for any alcohol-containing fuel, various sensors are required, such as an oxygen sensor for detecting a stoichiometric air-fuel ratio state, and an air flow sensor for predicting the air fuel ratio (A/F), as described in Japanese Patent Laid-Open No. Sho 63-5131.
In particular, FFV engine control described in Japanese Patent Laid-Open No. Sho 63-5131 is carried out in the following procedure.
First, a “stoichiometric air fuel ratio state” regarding an alcohol-containing fuel irrespective of the inclusion concentration of alcohols is detected by an oxygen sensor attached in an exhaust pipe of an engine, and the fuel injection amount is adjusted in response to a detected stoichiometric air fuel ratio state to control the air fuel mixture so as to achieve a desired stoichiometric air fuel ratio.
The air fuel ratio (A/F) in the stoichiometric air fuel ratio state is determined from an intake air mass (Ga) during operation predicted from a signal from a sensor for detecting the intake air mass such as an air flow sensor or an intake air negative pressure sensor and a fuel consumption amount (Gf) during operation predicted by integration of the fuel injection time within a fixed period of time.
Since the relationship between the alcohol concentration and the stoichiometric air fuel ratio is known in advance, the alcohol concentration can be predicted from the air fuel ratio (A/F).
A fuel of a mixture of the same combination of an intake air mass (Ga) and a fuel consumption amount (GO has a tendency that, as the alcohol concentration increases, the low calorific power decreases and the output power decreases. Accordingly, the appropriate ignition timing is retarded by a greater amount as the alcohol concentration increases. Taking such phenomena into consideration, as described above, a control map for the ignition timing is prepared for each alcohol concentration to allow appropriate FFV engine control.
Further, a technique is conventionally known which includes a crank pulse rotor which rotates in synchronism with a crankshaft of an engine and a pickup coil for detecting a passing state of reluctors (teeth) provided on the pulse rotor and can detect various states of the engine based on a pulse signal outputted from the pickup coil.
Japanese PatentLaid-Open No. 2002-115598 discloses a technique wherein a reluctor of a crank pulse rotor is provided at a position in the proximity of the top dead center of an engine and a ratio between a period of time in which the pulser rotor makes one rotation and a period of time in which the reluctor passes is calculated such that the load state of the engine is detected based on a degree of variation of the ratio.
However, in carrying out FFV engine control, a less expensive system which omits sensors to the utmost is demanded for a less expensive vehicle such as a motorcycle.
While the technique disclosed in Japanese Patent Laid-Open No. 2002-115598 detects the load state of an engine based on a state of rotation of a crankshaft to carry out ignition operation at a suitable timing, an application of the same to a configuration which can detect various values for carrying out engine control is expected.
It is one of the objects of the present invention to provide an alcohol concentration estimation and detection apparatus which solves the problems of the prior art as described above, and which eliminates the necessity for various sensors which have conventionally been required for detection of alcohol concentration, by estimating and detecting the alcohol concentration of an alcohol-containing fuel based on an output signal of a crank pulse rotor.